Decision Points: The Factors Influencing the Decision to Feed in the Medicinal Leech

Quentin Gaudry,William B Kristan

doi:10.3389/fnins.2012.00101

Quentin Gaudry, William B Kristan

Open Access

https://doi.org/10.3389/fnins.2012.00101

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Abstract

The decision to feed is a complex task that requires making several small independent choices. Am I hungry? Where do I look for food? Is there something better I’d rather be doing? When should I stop? With all of these questions, it is no wonder that decisions about feeding depend on several sensory modalities and that the influences of these sensory systems would be evident throughout the nervous system. The leech is uniquely well suited for studying these complicated questions due to its relatively simple nervous system, its exceptionally well-characterized behaviors and neural circuits, and the ease with which one can employ semi-intact preparations to study the link between physiology and decision-making. We will begin this review by discussing the cellular substrates that govern the decision to initiate and to terminate a bout of feeding. We will then discuss how feeding temporarily blocks competing behaviors from being expressed while the animal continues to feed. Then we will review what is currently known about how feeding affects long-term behavioral choices of the leech. Finally, we conclude with a short discussion of the advantages of the leech’s decision-making circuit’s design and how this design might be applicable to all decision circuits.

Highlights

To survive and obtain the necessary energy to fuel everyday life, animals must feed
We do not know which sensory neurons activate these serotonergic neurons, it is likely that the lip chemoreceptors (Elliott, 1986, 1987) are a major source because the suppression of other behaviors is observed during the exploration of a potential food item even before the leech begins to feed (Gaudry and Kristan, 2009) and when full strength artificial blood is presented at ambient temperature to the lip of head-intact isolated nerve cord prepa- (Groome et al, 1995; Zhang et al, 2000)
Decades of research on the feeding behavior of the medicinal leech have revealed the complex interactions between neuromodulators, sensory receptors, and the downstream targets that influence how the medicinal leech controls feeding behavior (Figure 4A)

Summary

Introduction

To survive and obtain the necessary energy to fuel everyday life, animals must feed. This universal drive makes feeding an ideal system for studying decision-making processes within the nervous system. To determine how the nervous system of a sanguivorous leech prevents mechanosensory stimuli from eliciting feeding-incompatible behaviors, we used a previously described semi-intact preparation (Wilson et al, 1996) that allows intracellular recordings to be made from the central nervous system while the rest of the animal is free to behave and most importantly, feed.

Results

Conclusion